W123 Differential Model Question - PeachParts Mercedes-Benz Forum

617collector · #1 04-22-2012, 10:53 PM

Hello All,

I just had an independent replace the differential on my 1984 300D. Since driving the car (picked it up Friday) I have noticed a sluggishness which is pronounced in city driving and under hard acceleration. The car also has trouble getting over 80 mph. A "quality" used unit was installed. Upon doing some research I came across there are several models with different ratios for these cars with two being implemented in 1984. My car was manufactured 10/84 thus supposedly using the faster version used in 1985. Does this sound correct? I am not well versed in the drivetrain area of the W123. The repair is unacceptable and will have to be followed up. Is there another part that might need adjusting or does this sound like an incorrect or bad differential? No fuel economy problems or rough power delivery. Just slow. All maintenance is up to date. Was superb before except for a whine.

Brian Carlton · #2 04-22-2012, 11:18 PM

The '84 would have been equipped with a 3.07 diff from the factory. The '85 is equipped with a 2.88. The difference is slight and the later diff will result in slightly slower off the line performance and slightly slower rpms on the highway. The top speed of the vehicle cannot be affected in any significant way by this change.

My guess is that the mechanic dislodged the pressure line to the ALDA while working under the hood for some reason that you have failed to mention.

None of the issues described in the post can be attributed to a diff change.

DeliveryValve · #3 04-23-2012, 12:15 AM

Quote:

Originally Posted by 617collector

Hello All,

.... My car was manufactured 10/84 thus supposedly using the faster version used in 1985. Does this sound correct?.....

If your car is manufactured 10/84, then it's a 1985 model year vehicle not an '84.

Perhaps the previous diff was a 3.07 and the mechanic replaced it with the correct 2.88. Which would lead to decrease performance in acceleration.

.

t walgamuth · #4 04-23-2012, 06:31 AM

...or perhaps he put in a 247 diff. that would be quite noticable. i think the difference between a 307 and a 288 would be tough to feel with the butt meter.

The ratio is stamped on the diff on the mating surface between the large part of the diff and the cover....on the left side is some extra metal where it appears.

617collector · #5 04-23-2012, 07:20 AM

Thanks for your replies. I made a mistake. My car was manufactured 10/83. What does the 247 feel like? I have owned a 1985 as well and it felt no different than my current '84.

vstech · #6 04-23-2012, 08:46 AM

what rpm is your motor turning at 60mph? if it's around 2500 rpm, then I go with brian's diagnosis, if it's around 1500rpm then you likely have a 224 or a 247 diff... which would be odd, as it would require changing the yoke to make it fit...

Brian Carlton · #7 04-23-2012, 09:15 AM

Quote:

Originally Posted by vstech

what rpm is your motor turning at 60mph? if it's around 2500 rpm, then I go with brian's diagnosis, if it's around 1500rpm then you likely have a 224 or a 247 diff... which would be odd, as it would require changing the yoke to make it fit...

3.07: 2750 rpm @ 60 mph
2.88: 2600 rpm @ 60 mph
2.47: 2250 rpm @ 60 mph

All of the above assume stock tires (24.7" diameter at the tread) and 250 rpm slip in the t/c (level ground).

t walgamuth · #8 04-23-2012, 09:32 AM

They also assume actual speed not what the possibly mismatched diff and speedo might read.

vstech · #9 04-23-2012, 09:44 AM

... duh. good point tom, the speedo and tach would read exactly the same... unless the mechanic changed the speedo along with the diff... which is unlikely. so my post is useless...
lets assume the 2.24 is in there, and it's taking you forever to reach 75mph... according to your speedometer. you would be traveling MUCH faster than indicated in that case, and you would be FLYING past other cars on the road. is that the case? or is the car simply sluggish, and refuses to gain power at all... in which case, the alda line is more likely the culprit, also possible is JUNK fuel got dumped into your tank, and the filters are plugged... accelerator linkage could be out of adjustment, or even disconnected...

Brian Carlton · #10 04-23-2012, 09:56 AM

Quote:

Originally Posted by vstech

... duh. good point tom, the speedo and tach would read exactly the same... unless the mechanic changed the speedo along with the diff... which is unlikely. so my post is useless...

Your post isn't useless. We just need to modify the data to show what the indicated speeds would be at the various rpm's. This makes the assumption that the vehicle originally had the proper 3.07 diff from the factory.

3.07: 2750 rpm @ 60 mph (indicated 60 mph)
2.88: 2600 rpm @ 60 mph (indicated 56 mph)
2.47: 2250 rpm @ 60 mph (indicated 48 mph)

The indicated readings are what the speedometer would show with the stock speedometer calibration and the various diffs installed at the actual speeds the vehicle is traveling.

I'd be very doubtful if they sourced a 2.24. The 2.47 is the most likely.

617collector · #11 04-23-2012, 03:18 PM

I have confirmed a 3.07 was installed and go the correct 2750 rpm at 60 mph. Going back to have the indy check it out. I inspected the ALDA system. Nothing out of place. Changed the differential fluid after 100 miles as instructed and found metal filings. My indy thinks it could be a bad unit thus under warranty. The original unit that had a whine did not have any metal shavings. I appreciate all you have added to my post. The saga continues.